In order for charts to work, the only items that qualify to be Values for charting are those that are going to be numeric, or in a couple reports, dates. The numeric value of those columns are what it uses to calculate the percentages of the pie chart that that Value represents for that particular report. Since "Health Name" is not a column that holds a numeric entry, it would have nothing to use to calculate the percentages of each pie "slice" that each Health Name would represent.
I hope this helps to clarify this reporting feature a little further. If you have any other questions please let me know.